TC: void setvect( int intr_num, void interrupt(*isr)() )

	- prototype in dos.h

	- sets the value of interrupt vector named by intr_num
	  (corresponds to 0-255 for MS-DOS) in DOS interrupt vector
	  table to a far pointer to "isr" an interrupt service routine
	- address of a C routine may be used only if it has been
	  declared to be an interrupt routine.	Ex:

void interrupt func( void );

	- MS C uses _dos_setvect()
	- see	INT 21,25